This study is about rehabilitation of arm function after a stroke. The investigators are testing the dosage of therapy that is needed for meaningful recovery of arm and hand function. Dosage of therapy refers to the amount of time (in this case, the total number of hours) that a person participates in treatment. The investigators hope to learn how much therapy time is needed in order for change to occur in arm and hand function after a person has had a stroke. Eligible candidates must have had a stroke affecting the use of an arm or hand at least 6 months ago.